In the Long Term Evolution (LTE) project developed from the 3rd Generation Partnership Project (3GPP), especially in view of the Time Division Duplex (TDD), the uplink Sounding Reference Signal (SRS) is adapted for obtaining the downlink Channel State Information (CSI) of corresponding frequency bands to perform channel quality sounding and to support operations such as downlink beam forming that is not fed back due to the symmetry of uplink and downlink channels. Moreover, the system can measure the channel information of the downlink channels of the bandwidth with which SRS can be transmitted.
Therefore in the prior art, SRS is transmitted with the bandwidth as wide as possible so as to support measurement of the channel information in the largest bandwidth of the downlink channel.
It is provided in the prior art that SRS generally can be located in the following two positions in LTE TDD:
1. the last symbol of the normal uplink subframe;
2. the Uplink Pilot Time Slot (UpPTS) of the special subframe.
FIG. 1 shows the frame structure of LTE TDD. As shown in FIG. 1, each radio frame consists of two half-frames each of which includes five subframes, i.e. each radio frame consists of ten subframes, e.g. subframe 0 to subframe 9 in the figure, wherein the subframe 1 and subframe 6 are special subframes comprising Downlink Pilot Time Slot (DwPTS), Guard Period (GP) and Uplink Pilot Time Slot (UpPTS), and the other subframes are normal subframes comprising normal uplink subframes.
UE transmits SRS with the largest bandwidth level informed by the system if the system informs to transmit SRS with the largest bandwidth level while SRS is located on the normal uplink subframe. As shown in FIG. 2, UE transmits SRS with the largest bandwidth level informed by the system which is, for example BW0_Normal.
The User Equipment (UE) will transmit SRS after extending the bandwidth of the largest level if the system informs to transmit SRS with the largest bandwidth level while SRS is located on UpPTS. Specifically, UpPTS may need to bear Physical Random Access Channel (PRACH). In case UpPTS bears PRACH, the interference between SRS and PRACH is avoided as they have to be completely separated in the frequency domain, which is referred to as frequency division multiplexing, in the UpPTS time slot. Thus, UE transmits SRS with the uplink system bandwidth not occupied by PRACH of UpPTS. Simply, SRS is transmitted with the bandwidth not occupied by PRACH of UpPTS in the uplink system bandwidth. UE transmits SRS with the overall uplink system bandwidth if UpPTS does not bear PRACH. As shown in FIG. 2, UE transmits SRS with the overall uplink system bandwidth when UpPTS does not bear PRACH, for example, the bandwidth is BW0_UpPTS in the figure. UE transmits SRS with the uplink system bandwidth not occupied by PRACH of UpPTS, when UpPTS bears PRACH, for example, the bandwidth is BW0_offPRACH (BW0_PRACH being deducted from BW0_UpPTS) in the figure. BW0_UpPTS thus is much larger than BW0_Normal, and the latter is the largest bandwidth informed by the system as mentioned above and will not cause the power limit produced by UE.
Upon researches and practice of the prior art, the inventor considers that the following problems exist in the prior art:
UE transmits SRS with the largest available bandwidth when SRS is located in UpPTS time slot in the prior art, i.e. the bandwidth with which SRS is transmitted is extended. The maximum transmitting power of UE, however, is generally constant in the unit time. The larger the transmitting bandwidth is in the unit time, the less the power is on the unit bandwidth. In this situation, power limit may occur for the UE with unfavorable channel environment, and this problem directly results in a lower signal-to-noise ratio detected on these bandwidths. Thus, these UE have poor capability of detecting the channel information with a low signal-to-noise ratio, thereby it is hard to accurately detect the channel information.